Recently, a so-called ink jet printer for recording by emitting an ink droplet and directly fitting it on a recording medium such as paper and a film is rapidly being popularized.
A so-called on-demand printer wherein an ink droplet is emitted according to a recording signal is particularly popularized of these ink jet printers because miniaturization and the reduction of the cost can be realized.
For a method of emitting an ink droplet in the above on-demand printer, various methods are proposed, however, a method of using a piezoelectric element or a method of using an exothermic element is popular. The former is a method of applying pressure to a pressure chamber filled with ink by the deformation of a piezoelectric element and emitting ink. The latter is a method of heating and boiling ink by an exothermic element and emitting ink by the pressure of generated foam.
For the above method of using a piezoelectric element, there are a method of bonding a laminated piezoelectric element formed by laminating three or more piezoelectric elements to a pressure chamber filled with ink via a diaphragm and pressurizing the pressure chamber via the diaphragm by linearly displacing the above laminated piezoelectric element and a method of bonding a piezoelectric element consisting of a single plate or a piezoelectric element in which two or more piezoelectric elements are laminated to a pressure chamber filled with ink via a diaphragm, curving the diaphragm by bimorph effect between the diaphragm and the piezoelectric element by applying voltage to the piezoelectric element and pressurizing the pressure chamber.
Such a printer is provided with a print head with the following structure for example. That is, as shown in FIG. 78, the print head is constituted by a pressure chamber forming part 1101, a diaphragm 1102, a piezoelectric element 1103 and a nozzle forming member 1104.
In the above pressure chamber forming part 1101, a first groove part 1105 forming a liquid supply passage, a second groove part 1106 forming a pressure chamber and a third groove part 1107 forming a liquid supply passage are formed so that they communicate and are open opposite to one main surface 101a. The first groove part 1105 and the third groove part 1107 are formed as grooves with approximately equal depth and the second groove part 1106 is formed as a deeper groove. In the above pressure chamber forming part 1101, a nozzle leading hole 1108 which is pierced from the bottom surface 1107a of the third groove part 1107 to a main surface 110b opposite to one main surface 101a of the pressure chamber forming part 1101 in the direction of thickness is formed.
A diaphragm 1102 is bonded to the side of one main surface 1101a of the above pressure chamber forming part 1101 by an adhesive not shown so that the diaphragm closes the first groove part 1105, the second groove part 1106 and the third groove part 1107, space surrounded by the first groove part 1105 and the diaphragm 1102 functions as a liquid supply passage 1109, space surrounded by the second groove part 1106 and the diaphragm 1102 functions as a pressure chamber 1110 and space surrounded by the third groove part 1107 and the diaphragm 1102 functions as a liquid passage 1111. Therefore, the liquid supply passage 1109, the pressure chamber 1110, the liquid passage 1111 and the nozzle leading hole 1108 are formed so that they communicate.
As an ink supply pipe not shown and connected to an ink tank not shown is attached to the above diaphragm 1102, a through hole not shown and corresponding to the ink supply pipe is made in the diaphragm 1102.
Further, a piezoelectric element 1103 consisting of a single plate is fixed by an adhesive not shown in a position corresponding to the pressure chamber 1110 of a main surface 1102a reverse to the surface opposite to the pressure chamber forming part 1101 of the above diaphragm 1102.
Furthermore, a nozzle forming member 1104 (hereinafter called an orifice plate 1104) in which an emission nozzle 1112 communicating with the nozzle leading hole 1108 for emitting ink is formed is arranged on one main surface 1101b reverse to one main surface 1101a which is the groove part open face of the pressure chamber forming part 1101.
That is, in the above print head, ink is supplied first from the liquid supply passage 1109 to the emission nozzle 1112 via the pressure chamber 1110, the liquid passage 1111 and the nozzle leading hole 1108 and a meniscus is formed at the end of the emission nozzle 1112. In the print head, as the piezoelectric element 1103 is contracted in an in-plane direction by bimorph effect when predetermined voltage is applied to the piezoelectric element and is curved in the direction of thickness shown by an arrow m.sub.1 in FIG. 78, the diaphragm 1102 is also curved in the direction shown by the arrow m.sub.1 in FIG. 78 according to the above curvature. As a result, the volume of the pressure chamber 1110 is decreased, pressure in the pressure chamber 1110 rises, ink is emitted from the emission nozzle 1112, the ink is fixed on a recording medium and printing is made.
Generally, such a printer is provided with such plural print heads. That is, as schematically shown in FIG. 79, such print heads are arranged so that they are parallel each other in the longitudinal direction of a tubular ink buffer tank 1114 provided with an ink supply port 1113 connected to an ink tank not shown and the liquid supply passage 1109 of each print head is connected to the ink buffer tank 1114 so that the liquid supply passage is perpendicular to the side 1114a of the ink buffer tank 1114. Therefore, the emission nozzle 1112 of each print head is open on one main surface. Ink is supplied from an ink tank not shown to the ink buffer tank 1114 and is supplied from there to the liquid supply passage 1109 of each print head.
Recently, documentation using a computer called desk top publishing is often performed particularly in an office and others and lately, a request for outputting not only a character and a graphic form but a color natural image such as a photograph together with a character and a graphic form is also increased. Accordingly, it is required to print high quality of a natural image and the reproduction of a halftone is important.
For a method of reproducing the above halftone in the above on-demand printer for emitting an ink droplet, various methods are proposed. That is, for a first method, a method of controlling the size of an emitted ink droplet by varying the voltage and the pulse length of a voltage pulse to be applied to a piezoelectric element or an exothermic element and representing a scale by varying the diameter of a print dot can be given.
However, according to this method, as ink cannot be emitted when voltage and pulse length applied to a piezoelectric element or an exothermic element are lowered/decreased too much, the minimum diameter of an ink droplet is limited, the number of representable scales is small, particularly the representation of a low-density image is difficult and the method is not enough to print a natural image.
For a second method, a method of constituting one picture element by a matrix consisting of (4.times.4) dots for example without varying a dot diameter and representing a scale in units of matrix using a so-called dither method can be given. In this case, representation in 17 scales is allowed.
However, if for example, printing is made in the same dot density as in the first method by this method, resolution is one fourth of that in the first method and as roughness is remarkable, the method is not enough to print a natural image.
The inventors of the present invention have proposed a printer wherein the density of an emitted ink droplet can be varied and the density of a printed dot can be controlled by mixing ink and a diluent solvent when ink is emitted and a natural image is printed out without deteriorating resolution.
Briefly describing the print head of such a printer mixing two solutions, the print head is constituted so that it is provided with an emission nozzle into which an emitted medium is led and a quantity determining nozzle into which a quantity determined medium is led so that they are adjacent, and the quantity determined medium and the emitted medium are mixed and emitted in the in-plane direction of the emission nozzle and the quantity determining nozzle by percolating a predetermined quantity of quantity determined medium into the emission nozzle from the quantity determining nozzle, mixing the quantity determined medium with the emitted medium in the vicinity of the opening of the emission nozzle and pushing out the emitted medium together with the emitted medium mixed with the quantity determined medium from the emission nozzle. In such a printer, a natural image is printed out by changing the quantity of a quantity determined medium which is either ink or a diluent solvent and changing the density of a dot by changing the mixing ratio of the ink or the diluent solvent. Either of the above quantity determined medium or the above emitted medium may be ink and the other may be a diluent solvent.
In such a two solution mixed type printer, a function for emitting ink or a diluent solvent is also required as in the above on-demand ink jet printer and for such a function for emission, the above method of using a piezoelectric element as in the above ink jet printer or the above method of using an exothermic element is popularly used.
Therefore, the above two solution mixed type printer is provided with approximately the same constitution as the above ink jet printer. An example in which a diluent solvent is an emitted medium and ink is used as a quantity determined medium will be described below. That is, a first liquid supply passage for leading an emitted medium into the above pressure chamber forming part, a first pressure chamber, a first liquid passage and a first nozzle leading hole are provided in order, a second liquid supply passage for leading a quantity determined medium, a second pressure chamber, a second liquid passage and a second nozzle leading hole are provided in order at a predetermined interval from these so that they are adjacent, a diaphragm is bonded to the pressure chamber forming part and a piezoelectric element is provided in a position corresponding to each pressure chamber.
Further, an orifice plate provided with an emission nozzle and a quantity determining nozzle respectively communicating with the first and second nozzle leading holes in a position corresponding to the first and second nozzle leading holes of the pressure chamber forming part is bonded to the main surface on the side on which a diaphragm is not arranged of the pressure chamber forming part. It is desirable that the orifice plate is formed so that the respective openings of the emission nozzle and the quantity determining nozzle are adjacent to facilitate the mixture of ink and a diluent solvent.
Generally, the above two solution mixed type printer is also provided with plural print heads and a first liquid supply passage and a second liquid supply passage of each print head are respectively connected to a diluent solvent buffer tank and an ink buffer tank. In the above printer, each print head is also arranged in parallel at a predetermined interval and each nozzle is arranged so that it forms a plane.
At this time, the diluent solvent buffer tank and the ink buffer tank are respectively connected to a diluent solvent tank and an ink tank, a diluent solvent or ink is supplied from the diluent solvent buffer tank or the ink tank to the first liquid supply passage or the second liquid supply passage, supplied to the first pressure chamber or the second pressure chamber and supplied to the emission nozzle or the quantity determining nozzle via the first liquid passage and the first nozzle leading hole or the second liquid passage and the second nozzle leading hole.
Also in the two solution mixed type printer, for example ink is percolated from the quantity determining nozzle to the emission nozzle as a quantity determined medium by applying predetermined voltage to a piezoelectric element, for example a diluent solvent is emitted from the emission nozzle as an emitted medium and ink and a diluent solvent is mixed and emitted, a mixed droplet is fixed on a recording medium and printing is made. Of these two solution mixed type printers, a printer using a diluent solvent for an emitted medium and using ink for a quantity determined medium is called a "carrier jet" printer.
In the above ink jet printer and the above "carrier jet" printer, liquid such as ink and a diluent solvent is required to be filled without foam in the corresponding pressure chamber and therefore, in a process in which a diaphragm is bonded to a pressure chamber forming part, high precision adhesion technique is requested.
For example, describing an ink jet printer shown in FIG. 78 as an example, for a method of bonding a diaphragm 1102 to a pressure chamber forming part 1101, a method of forming the diaphragm 1102 using material provided with photosensitivity and adhesive property such as dry film resist and bonding the above diaphragm 1102 on the side of one main surface 1101a of the pressure chamber forming part 1101 by heating and pressing the diaphragm after a first groove part 1105 forming a liquid supply passage 1109 and a third groove part 1107 forming a liquid passage 1111 are formed in the pressure chamber forming part 1101 can be given and is heretofore often used.
However, when this method is adopted and the diaphragm 1102 is bonded to the pressure chamber forming part 1101, there are problems that a high-priced exposer is required and further, thermosetting processing is required so as to provide durability to ink, a diluent solvent and others to dry film resist forming the diaphragm 1102.
For a method of bonding the diaphragm 1102 to the pressure chamber forming part 1101, a method of forming the pressure chamber forming part 1101 and the diaphragm 1102 by glass material and executing anodic bonding of the diaphragm 1102 to the pressure chamber forming part 1101 can be also given. However, as glass material is weak in an impulse and a flaw, it is difficult in this method to thin the thickness of the diaphragm 1102 so that it is 10 .mu.m or less.
If pressure required to emit ink from an emission nozzle 1112 is generated in a pressure chamber 1110, a load according to the thickness of the diaphragm 1102 is generated in a piezoelectric element 1103. Therefore, the diaphragm 1102 is required to be thinned so as to reduce voltage for driving the piezoelectric element 1103, however, as it is difficult in the above method to thin the diaphragm 1102 in a printer wherein the diaphragm 1102 is bonded to the pressure chamber forming part 1101, driving voltage cannot be reduced. In such a printer, the width of the pressure chamber 1110 is required to be widened so as to decrease the load of the piezoelectric element 1103, it is difficult to miniaturize the pressure chamber 1110, that is, to decrease pitch between emission nozzles 1112 and it is also difficult to miniaturize such a printer.
Further, for a method of bonding the diaphragm 1102 to the pressure chamber forming part 1101, a method of bonding the pressure chamber forming part 1101 and the diaphragm 1102 using an adhesive can be also given and is heretofore used. However, as it is difficult in this method to apply an adhesive so that it is 2 .mu.m or less, there are problems that the first and third groove parts 1105 and 1107 may be blocked by an adhesive if the depth of the first groove part 1105 forming the liquid supply passage 1109 and the third groove part 1107 forming the liquid passage 1111 respectively formed in the pressure chamber forming part 1101 is shallow and the passage characteristics of the liquid supply passage 1109 and the liquid passage 1111 are changed.
For a method of solving such problems, a method of using a silicon substrate and others for the material of the pressure chamber forming part 1101 and enhancing the aspect ratio (the ratio of depth to width) of the first groove part 1105 forming the liquid supply passage 1109 and the third groove part 1107 forming the liquid passage 1111 by etching the pressure chamber forming part 1101 by anisotropic etching can be given.
However, as in this method, the material of the other members is required to be selected according to the thermal expansion coefficient of silicon if silicon is used for the material of the pressure chamber forming part 1101, there is a problem that the allowable range of selecting material is extremely limited.
For a method of bonding the diaphragm 1102 to the pressure chamber forming part 1101, as disclosed in Japanese published unexamined patent application No. H5-183625, a method of using a thermoplastic bonding sheet for an adhesive for bonding the diaphragm 1102 to the pressure chamber forming part 1101 can be also given. However, in this method, a through hole for correcting the overflow of an adhesive is required to be formed through the bonding sheet before a bonding process so as to prevent the overflow of the adhesive from blocking an ink supply port and high precision is required for the alignment and dimensional precision. Further, there are problems that the strength of one bonding sheet is not high and high precision temperature control is required to maintain the precision.
That is, the target of a two solution mixed type printer such as such an ink jet printer and such a "carrier jet" printer is the facilitation of operation for bonding a diaphragm to a pressure chamber forming part in which a pressure chamber is formed without blocking a liquid supply passage formed on the side of one main surface of the pressure chamber forming part.
Furthermore, in these printers, as a diaphragm is displaced every emission of liquid, a mechanical load is applied to a part in which the diaphragm is bonded every emission of liquid, peeling and others may be caused in the part in which the diaphragm is bonded and greatly deteriorates a function as a printer.
To solve such problems, the inventors have proposed a printer wherein a diaphragm is formed by thermoplastic material and thermocompression bonding is applied between the diaphragm and a pressure chamber forming part to enhance an adhesive property between them. However, when the above printer is manufactured, a process in which the diaphragm is bonded to the pressure chamber forming part to which an orifice plate after an emission nozzle and a quantity determining nozzle are formed is bonded is executed, and temperature and pressure for enabling the thermocompression bonding of thermoplastic material are also applied to the orifice plate in which the nozzles are already formed.
In such a printer, it is desirable that a liquid repelling film is formed in the periphery of the opening of a nozzle in an orifice plate to stabilize the emitted direction of a droplet. As the liquid repelling film may block a nozzle when the liquid repelling film is formed after a nozzle is formed, it is desirable that the liquid repelling film is formed before a nozzle is formed. That is, in such a printer, temperature and pressure for enabling the thermocompression bonding of thermoplastic material are also applied to the liquid repelling film.
Therefore, if a diaphragm formed by thermoplastic material is bonded to a pressure chamber forming part by thermocompression bonding after a liquid repelling film is formed, heat resistance is requested for the liquid repelling film to prevent the shape of the periphery of the opening of a nozzle from being changed, resistance to peeling is requested to prevent the liquid repelling film from adhering to a jig and severer performance is required, compared with an actual service condition.
A method of executing liquid repelling processing in the periphery of the opening of a nozzle on the surface on which nozzles are open of an orifice plate after a diaphragm formed by thermoplastic material is bonded to a pressure chamber forming part to which the orifice plate in which nozzles are formed is bonded can be also considered, however, as the opening of a nozzle may be blocked, the realization is difficult.
The present invention makes it the object to secure the bonding strength of a diaphragm, to enable using a liquid repelling film provided with liquid repelling performance according to an actual service condition and also to enable widening a range in which the liquid repelling film is selected in a two solution mixed type printer such as the above ink jet printer and the above "carrier jet" printer.